1. Field of the Invention
The present invention relates to a process for producing a chip.
2. Description of the Related Art
As an example of a liquid ejection head from which a liquid is ejected, an ink jet recording head used in an ink jet recording system is mentioned. The ink jet recording head has a chip generally provided with a flow path, a heat-generating element provided in a part of the flow path for generating energy for ejecting an ink, and a minute ink ejection orifice for ejecting the ink. A process for producing such a chip includes the following steps:    a step of forming a pattern of a flow path with a photosensitive material on a substrate on which a heat-generating element has been formed and then applying and forming a coating resin layer which will become a flow path forming member with a photosensitive material on the substrate so as to coat the pattern; and    a step of forming an ejection orifice in the coating resin layer obtained in the above step and then removing the photosensitive material used in the pattern to form the flow path.
According to this production process, minute processing as to the formation of the flow path and the ejection orifice becomes feasible with extremely high accuracy because a photolithographic method used in a semiconductor field is applied thereto. In this production process, patterning by exposure by means of a semiconductor exposure apparatus is used as a method for forming the photosensitive material into an intended shape upon the formation of the ejection orifice. When a negative photosensitive material is used, a shadow is prepared into a shape intended to be formed by, for example, a reticle, and exposure is conducted through the semiconductor exposure apparatus, whereby the photosensitive material of a portion where the shadow has been prepared and light has not been applied is not cured and removed in a removal step.
On the other hand, as a process for improving the productivity of a chip, a process in which a great number of liquid ejection heads are fabricated as chips on a wafer such as an Si wafer, and respective chips are divided by cutting to obtain individual liquid ejection heads is used. According to this process, the plural chips can be treated successively or at a time under the same conditions in the respective production steps, and so the efficiency of production can be improved. For example, when an intended structure is fabricated in the respective chips by exposure and development for the photosensitive material, exposure of the same exposure pattern can be successively conducted for the respective chips by means of a reticle of an exposure apparatus, whereby the exposure treatment can be conducted with good efficiency.
In recent years, the length of a chip has been made longer for achieving high-speed printing. In addition, the number of ejection orifice arrays (also referred to as nozzle arrays) taking charge of different colors is also increased with the increase in the kinds of inks for expanding a color gamut in photo-printing, and the breadth of the chip is also widened owing to the increase in the nozzle arrays corresponding to respective colors. As a result, an area per chip comes to increase. Under such circumstances, a pattern is arranged for use up to the neighborhood of the margin of a field angle of a reticle for the purpose of exposing plural chips at a time for shortening process time and reducing the number of times of exposure. As a result, when reduction projection exposure is conducted, light transmitted through a portion high in curvature of a lens in a projection lens system within a semiconductor exposure apparatus is influenced by lens aberrations to greatly affect the finish of ejection orifice formation in some cases. It means that when the light from the semiconductor exposure apparatus is adjusted so as to exactly form a pattern utilizing a part around a center of the reticle, exposure is conducted at a position of outside distortion with respect to an ideal lattice with increasing distance from the part around the center of the reticle. An example thereof is typically illustrated in FIGS. 1A and 1B. FIG. 1A illustrates ideal lattice patterns provided on the whole surface within the field angle of the reticle, and a solid-line portion becomes a light shielding portion. FIG. 1B illustrates that a pattern obtained in the case where the exposure is conducted by means of this reticle and formed of an actual light shielding portion on an object to be exposed has a portion distorted from the ideal lattice pattern. That is to say, when a pattern is formed in the neighborhood of the margin of a field angle of a reticle of a stepper exposure apparatus, and a chip is exposed to light having passed through that pattern to form an ejection orifice, there has been caused such a problem that the position of the ejection orifice deviates outside from the center of the reticle.
Regarding such an optical problem, Japanese Patent Application Laid-Open No. 2001-264637 (Patent Literature 1) discloses means for basically correcting the above-described aberrations by devising a lens system. According to this means, a spherical aberration-correcting optical system is installed in the inside and detachably mounted on the side of an image of an objective lens, and a lens group closest to the side of an object has negative refracting power and is moved in a direction of an optical axis, whereby the spherical aberration can be corrected.